1. Field of the Invention
The present invention relates to a fuel hose and, more particularly, to a fuel hose for automobile fuel line.
2. Description of the Art
Fuel hoses are conventionally used for automobile fuel line. Typically, such a fuel hose is of a single layer structure or of a multi-layer structure having two or more layers. An inner layer of the fuel hose to be in contact with a fuel is composed of a polyamide resin (nylon), a fluororesin or the like. The polyamide resin serves as a barrier against ordinary gasoline fuel, but has an extremely poor barrier property against so-called gasohol (a mixture of a gasoline and an alcohol). On the other hand, the fluororesin has an excellent barrier property against gasoline fuel and gasohol, but is an expensive material which thereby leads to an increase in production costs. In this connection, polyester resins attract attention as a resin material which are less expensive than a fluororesin and have a better barrier property against gasohol than a polyamide resin and, it has been proposed that a fuel hose be produced by employing polybutylene terephthalate (PBT).
PBT generally has a better barrier property against gasohol than a conventional polyamide resin, but is still insufficient in barrier property when evaluated on stricter criteria which requires a further improved gasohol permeation resistance. In the future, it will be environmentally preferred to use a gasohol containing gasoline and an alcohol (methanol, ethanol or the like) as an automobile fuel for cleaner automobile emissions. Therefore, these fuel hoses are required to have a more effective barrier property against gasohol. In the meantime, the present applicant suggested a fuel hose comprising polybutylene naphthalate (PBN) for improvement of gasohol permeation resistance (Japanese Patent Unexamined Publication No. 2000-154890). However, it was found that this fuel hose had some problems in a viewpoint of hydrolytic resistance.
In view of the foregoing, it is an object of the present invention to provide a fuel hose which is excellent in gasohol permeation resistance and hydrolytic resistance.
In accordance with the present invention to achieve the aforesaid object, there is provided a fuel hose which comprises at least one layer including an inner layer composed of a resin composition, the resin composition essentially comprising a polyester resin including at least one of polybutylene naphthalate and polyethylene naphthalate and further comprising a phosphate.
The inventors of the present invention have conducted studies on a material for a fuel hose inner layer to provide a fuel hose having an excellent gasohol permeation resistance and hydrolytic resistance. As a result, the inventors have found that an inner layer composed of a resin composition comprising at least one of polybutylene naphthalate (PBN) and polyethylene naphthalate (PEN) among other polyester resins, provides a better gasohol permeation resistance than a conventional inner layer composed of PBT, and also have found that when the inner layer is composed of a resin composition which includes a phosphate in addition to the above polyester resin, the hose has an improved hydrolytic resistance, and then attained the present invention. This better gasohol permeation resistance is supposedly because PBN and PEN each have a higher crystallinity and a greater molecular size than PBT and thus provide a higher barrier effect. In general, the terminal carboxyl groups of the polyester resin are liable to influence the hydrolysis of the polyester resin. Since the phosphate blended in the resin composition reacts with these terminal carboxyl groups to prevent these carboxyl groups from functioning as a hydrolytic catalyst, the hydrolysis of the polyester resin is suppressed to thereby improve the hydrolytic resistance.
When the fuel hose is constituted by a single layer, the term xe2x80x9cinner layerxe2x80x9d means the single layer itself. When the fuel hose is of a multi-layer structure having two or more layers, the term xe2x80x9cinner layerxe2x80x9d means the innermost layer of the hose.